Backside Redistribution Layer (RDL) Structure

ABSTRACT

An embodiment package on package (PoP) device includes a molding compound having a metal via embedded therein, a passivation layer disposed over the molding compound, the passivation layer including a passivation layer recess vertically aligned with the metal via, and a redistribution layer bond pad capping the metal via, a portion of the redistribution layer bond pad within the passivation layer recess projecting above a top surface of the molding compound.

BACKGROUND

As the demand for smaller electronic products grows, manufacturers andothers in the electronics industry continually seek ways to reduce thesize of integrated circuits used in the electronic products. In thatregard, three-dimensional (3D) type integrated circuit (IC) packagingtechniques have been developed and used.

One packaging technique that has been developed is Package-on-Package(PoP). As the name implies, PoP is a semiconductor packaging innovationthat involves stacking one package on top of another package. A PoPdevice may combine vertically discrete memory and logic packages. Insome cases, the PoP device is referred to an integrated fan-out (InFO)PoP device because the contact positions of the original die are “fannedout” to a larger foot print.

If not appropriately or suitably formed, the InFO PoP devices may besubject to electrical failures or have poor reliability. For example,the InFO PoP devices may experience crack propagation or suffer ballfatigue.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an embodiment package on package (PoP) deviceutilizing protruding redistribution layer bond pads;

FIGS. 2A-2D illustrate embodiments of the redistribution layer bond padsin the PoP device of FIG. 1 capping metal vias;

FIG. 3 illustrates dimension lines and angles pertaining to embodimentredistribution layer bond pads; and

FIGS. 4A-4T collectively schematically illustrates a process flow usedto manufacture the embodiment PoP device 10 utilizing the protrudingredistribution bond pads of FIG. 1.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the disclosure providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, namely a three dimensional (3D) integrated fan-out(InFO) package-on-package (PoP) device. The concepts in the disclosuremay also apply, however, to other semiconductor structures or circuits.

Referring now to FIG. 1, an embodiment PoP device 10 is illustrated. Asshown, the PoP device 10 includes a top package 12 electrically coupledto a bottom package 14 using a protruding redistribution layer bond pad16. As will be more fully explained below, the protruding orupwardly-projecting redistribution layer bond pad 16 provides numerousadvantages and benefits for the PoP device 10 relative to other PoPdevices. For example, the protruding redistribution layer bond pad 16permits a backside redistribution layer (RDL) to be formed in anIntegrated Fan Out Package on Package (InFO PoP) device, prevents cracksfrom occurring or propagating within the PoP device (e.g., between themolding compound and the metal via, at the backside RDL polymer, etc.),and so on.

As shown in FIG. 1, the top package 12 is mounted above the bottompackage 14 in the embodiment PoP device 10. The top package 12 mayinclude one or more dies 18. In an embodiment, the dies 18 arevertically discrete memory components. For example, each of the dies 18may be a memory component such as, for example, a dynamic random accessmemory (DRAM) or another suitable type of memory. While two of the dies18 are depicted in FIG. 1, more or fewer of the dies 18 may be includedin other embodiments.

In an embodiment, the dies 18 in the top package 12 are electricallycoupled to the bottom package 14 through wiring bonding as well as viasand contact pads in a top package substrate 20. The top package 12 mayinclude molding compound 22 or another suitable encapsulant to cover thedies 18 and protect the wire bonding connections. In practicalapplications, each of the top and bottom packages 12, 14 may includevarious other components, layers, circuits, and structures that havebeen omitted herein for the sake of brevity.

The bottom package 14 has a front side 24 and a backside 26. At thefront side 24, the bottom package 14 includes a bottom package substrate28. In an embodiment, the bottom package substrate 28 is apolybenzoxaxole (PBO) or other suitable substrate material. As shown inFIG. 1, a number of solder features 30 are mounted to the bottom packagesubstrate 28. In an embodiment, the solder features 30 are solder ballsfrom a ball grid array (BGA). As shown, the solder features 30 permitthe bottom package 14 to be mounted and electrically coupled to, forexample, an underlying printed circuit board (PCB) 32 or othercomponent.

The bottom package substrate 28 includes a front side redistributionlayer 34. The frontside RDL 34 electrically couples a die 36 in thebottom package 14 to, for example, the solder features 30 and the PCB32. In an embodiment, the die 36 in the bottom package 36 is a logicdevice or logic component (a logic integrated circuit, analog circuit,and so on). While one of the dies 36 is depicted in FIG. 1, it should berecognized that more of the dies 36 may be included in otherembodiments. In an embodiment, the die 36 is encapsulated by moldingcompound 38 or another suitable encapsulant to cover the die 36.

In an embodiment, the die 36 is mounted beneath or to a passivationlayer 40 using a die attach film (DAF) 42. In an embodiment, thepassivation layer 40 comprises polybenzoxaxole (PBO), an Ajinomotobuild-up film (ABF), or other suitable material. A buffer layer 44 maybe disposed over the passivation layer 40. In an embodiment, the bufferlayer 44 comprises PBO, an ABF, or other suitable material. Optionally,a laminating tape 46 may be disposed over the buffer layer 44. Whenused, the laminating tape 46 comprises a solder release (SR) film, anABF, a backside laminating coating tape (LC tape) comprising athermosetting polymer, or other suitable material.

In an embodiment, an underfill material 48 may be used to encapsulateportions of the top and bottom packages 12, 14 as shown in FIG. 1. Theunderfill material 48 may extend from a top surface of the PCB 32, alongsides of the bottom package 14, and along a portion of the sides of thetop package 12. In an embodiment, the underfill material 48 is onlydisposed between the top package substrate 20 and the laminating tape 46or the buffer layer 44 if the laminating tape 46 was not used.

Still referring to FIG. 1, the bottom package 14 also includes throughpackage vias (TPV) 50 extending between the front side 24 and thebackside 26 of the bottom package 14. The through package vias 50, whichmay also be referred to herein as through InFO vias (TIVs) or metalvias, are embedded in and pass through the molding compound 38. In anembodiment, the through package vias 50 comprise copper, nickel (Ni), acopper alloy (copper/titanium), solder, a solder alloy includingtin-silver (SnAg), tin-bismuth (SnBi), tin-copper (SnCu),tin-silver-copper (SnAgCu), tin-silver-copper-nickel (SnAgCuNi), orcombinations thereof, or another metal. While six of the through packagevias 50 are illustrated in FIG. 1, more or fewer of the through packagevias 50 may be included in other embodiments.

The bottom package 14 also includes a backside redistribution layer 52.As shown, a portion of the backside redistribution layer (RDL) 52extends over a top surface of the die 36. As such, the die 36 iselectrically coupled to, for example, the dies 18 in the top package 12and the through package vias 50. In addition, another portion of thebackside redistribution layer 52 extends over the through package vias50. In particular, the protruding redistribution layer bond pads 16 fromthe backside redistribution layer 52 are disposed on the upper portionsof the through package vias 50. As will be more fully explained below,the protruding redistribution layer bond pads 16 cap or otherwise coverthe top of the through package vias 50 in FIG. 1. In an embodiment, theprotruding redistribution layer bond pads 16 and the through packagevias 50 are formed from the same material (e.g., copper). As such, theprotruding redistribution layer bond pads 16 and the through packagevias 50 may appear to be a single unitary structure.

Solder features 54 are formed or mounted on, and electrically coupledto, the protruding redistribution layer bond pads 16. The solderfeatures 54 electrically couple the top package 12 with the bottompackage 14. In an embodiment, the solder features 54 are formed fromsolder paste, organic solderability preservative (OSP), or othersuitable conductive material, or combinations thereof. In an embodiment,an intermetallic compound (IMC) 56 is disposed between the solderfeatures 54 and the underlying redistribution layer bond pads 16 cappingthe through package vias 50. The intermetallic compound 56 is a productof a reflow process used to electrically couple the solder feature 54and the through package vias 50.

Referring now to FIGS. 2A-2D, embodiments of the redistribution layerbond pads 16 capping the through package vias 50 are depicted in furtherdetail. For the purposes of illustration, the solder feature 54 from thePoP device 10 (see FIG. 1) has been omitted.

In FIG. 2A, the through package vias 50 are embedded in the moldingcompound 38. The through package vias 50 extend from the redistributionlayer bond pad 16 of the backside redistribution layer 52 to the frontside redistribution layer 34 in the bottom package substrate 28. Thepassivation layer 40 is disposed over the molding compound 38 and thebuffer layer 44 and the optional tape layer 46 are disposed over thepassivation layer 40. As shown, a recess 58 extends through thepassivation layer 40, the buffer layer 44, and the optional tape layer46. The recess 58 is vertically aligned with the underlying throughpackage via 50.

The redistribution layer bond pad 16 in FIG. 2A caps or otherwise coversthe top surface of the through package via 50. Moreover, a portion ofthe redistribution layer bond pad 16 projects or extends above a topsurface of the molding compound 38. In an embodiment, the centralportion of the redistribution layer bond pad 16 protrudes or projectsupwardly into the recess 58 while outer portions of the redistributionlayer bond pad 16 are embedded in the molding compound 38. In otherwords, in an embodiment the redistribution layer bond pad 16 has anon-linear profile.

As shown, sidewalls of the portion of the redistribution layer bond pad16 projecting above the top surface of the molding compound 38 arespaced apart from sidewalls of the laterally adjacent passivation layer40. In an embodiment, a redistribution layer bond pad diameter D2 isgreater than a metal via diameter D1. In addition, and as will be morefully explained below, no seed metal is disposed between the throughpackage via 50 and the redistribution layer bond pad 16 in theembodiment of FIG. 2A.

Referring now to FIG. 2B, a first redistribution layer bond pad 16 acaps the metal via 50. In addition, a second redistribution layer bondpad 16 b is vertically spaced apart from the first redistribution layerbond pad 16 a by a portion of the passivation layer 40. As shown, aportion of the second redistribution layer bond pad 16 b within therecess 58 projects upwardly away from the molding compound 38 and theunderlying metal via 50. In an embodiment, a first redistribution layerbond pad diameter D2 and a second redistribution layer bond pad D3 areeach greater than a metal via diameter D1.

Referring now to FIG. 2C, the redistribution layer bond pad 16 caps themetal via 50. However, unlike the embodiment in FIG. 2A, a portion ofthe passivation layer 40 is disposed between the redistribution layerbond pad 16 and the metal via 50. In an embodiment, the redistributionlayer bond pad diameter D2 is greater than the metal via diameter D1.

Referring now to FIG. 2D, the first redistribution layer bond pad 16 acaps the metal via 50. However, a portion of the passivation layer 40 isdisposed between the first redistribution layer bond pad 16 a and themetal via 50. In addition, the second redistribution layer bond pad 16 bis vertically spaced apart from the first redistribution layer bond pad16 a by another portion of the passivation layer 40. As shown, a portionof the second redistribution layer bond pad 16 b within the recess 58projects upwardly away from the top surface of the molding compound 38and the metal via 50. In an embodiment, the first redistribution layerbond pad diameter D2 and the second redistribution layer bond pad D3 areeach greater than the metal via diameter D1.

Referring now to FIG. 3, the embodiment redistribution layer bond pad 16and metal via 50 depicted in FIG. 2A has been reproduced with dimensionlines and angles, which may apply to the various embodiments describedherein. In an embodiment, a diameter d1 of a top surface of theredistribution layer bond pad is less than or equal to a diameter d2 ofa sidewall base of the redistribution layer bond pad.

In an embodiment, a profile angle θ₂ of the redistribution layer bondpad, which is defined by sidewalls and a plane extending between a topsurface of bond pad legs, is between about forty degrees and aboutninety degrees. In an embodiment, a height h2 of the redistributionlayer bond pad disposed above the molding compound 38 is greater than orequal to a height h1 of the passivation layer. In an embodiment, theheight h2 is between about 1 μm and about 15 μm.

In an embodiment, the diameter d1 satisfies the formula: d1=d2−2[h1(tanθ2)], where d2 is the diameter of the sidewall base of theredistribution layer bond pad, h1 is the height of the passivationlayer, and θ₂ is the profile angle of the redistribution layer bond paddefined by sidewalls and a plane extending between a top surface of bondpad legs. In an embodiment, the diameter d1 is between about 65 μm andabout 290 μm.

In an embodiment, the diameter D2 of the redistribution layer bond padis greater than or equal to the diameter d2 of a sidewall base of theredistribution layer bond pad. In an embodiment, diameter D2 is betweenabout 30 μm and about 380 μm. In an embodiment, diameter d2 is betweenabout 80 μm and about 300 μm.

In an embodiment, the diameter D1 of the metal via 50 is less than orequal to the diameter d2 of a sidewall base of the redistribution layerbond pad. In an embodiment, diameter D1 is between about 80 μm and about300 μm. In an embodiment, diameter d2 is between about 80 μm and about300 μm. In an embodiment, the protruding redistribution layer bond pad16 has a roughness (Ra) of between about 0.2 μm to about 1 μm.

In an embodiment, a diameter d3 at the top of the recess 58 (which existin the tape layer 46, the buffer layer 44, or the passivation layer 40depending on the layers used for fabrication of the PoP device 10) isgreater than a diameter d4 at the bottom of the recess 58. In otherwords, the recess 58 gets progressively wider from bottom to top and atop opening of the recess 58 is greater than a bottom opening of therecess 58.

In an embodiment, a height h3 of the tape layer 46, the buffer layer 44,and/or the passivation layer 40 (depending on the layers used forfabrication of the PoP device 10) is greater than the height h2 of theredistribution layer bond pad 16 disposed above the molding compound 38.If, however, a portion of the passivation layer 40 is disposed beneaththe redistribution layer bond pad 16 (see, for example, FIG. 2B), thenthe height h2 is measured from a top surface of the laterally extendinglegs of the redistribution layer bond pad 16. In an embodiment, theheight h3 is between about 1 μm and about 55 μm. In an embodiment, anopen profile angle θ₁ of the recess 58, which is defined by sidewalls ofthe recess 58 and a top surface of legs of the redistribution layer bondpad 16, is between about forty degrees and about seventy degrees.

FIGS. 4A-4T collectively schematically illustrate a process flow used tomanufacture the embodiment PoP device 10 utilizing the protrudingredistribution bond pads 16 as shown in FIGS. 1 and 2A. In FIG. 4A, aglue layer 60 and the buffer layer 44 are deposited over a carrier 62.In FIG. 4B, the passivation layer 40 is deposited over the buffer layer44 and then patterned. In FIG. 4C, a seed metal 64 is deposited over thepatterned passivation layer 40. In an embodiment, the seed metal 64 iscopper, a copper alloy (e.g., copper/titanium), or another metal.

In FIG. 4D, a photo resist (PR) 66 is deposited over the seed metal 64and patterned so that the backside redistribution layer may be formed.In FIG. 4E, the backside redistribution layer 52, including theredistribution layer bond pads 16, is formed. As shown in FIG. 4E, theredistribution layer bond pads 16 have a non-linear or non-linearprofile. In an embodiment, the method may be modified to form theredistribution layer bond pads 16 shown in FIGS. 2B-2D by, for example,using additional metal layers or material, depositing additionalpassivation layers or material, and so on.

In FIG. 4F, the photo resist 66 is stripped away or otherwise removed toexpose the redistribution layer 52, which includes the redistributionlayer bond pads 16 In FIG. 4G, a dry film release (DFR) layer 68 isdeposited and patterned so that the through package vias (a.k.a., thethrough InFO vias) may be formed. In an embodiment, the dry film releaselayer 68 is deposited through a lamination process.

In FIG. 4H, the through package vias 50 are formed in the openingsdefined by the dry film release layer 68. Thereafter, as shown in FIG.4I, the dry film release layer 68 is stripped away or otherwise removed.In addition, an under bump metallization (UBM) process is performed toremove portions of the seed layer 64 disposed beyond the redistributionlayer 52. In FIG. 4J, the die 36 (a.k.a., chip) is placed. In anembodiment, the die 36 is mounted to the exposed passivation layer 40using the die attach film 42.

Next, as shown in FIG. 4J, the molding compound 38 is deposited over thedie 36 and the through package vias 50 (a.k.a., through InFO vias, metalvias). As shown in FIG. 4K, a mold grinding process is performed toremove a top portion of the molding compound 38 and expose the metalvias 50 and contacts on the exterior surface of the die 36. In FIG. 4M,the front side redistribution layer 34 and the under bump metallization(UBM) is formed and then covered by the bottom package substrate 28.

In FIG. 4N, solder features 30 (e.g., solder balls from a BGA) aremounted and electrically coupled to the under bump metallization. In anembodiment, testing is performed at this stage to ensure the bottompackage 14 has been suitably formed. Thereafter, the bottom package 14is de-bonded from the carrier 62 and flipped over as shown in FIG. 4O.

In FIG. 4P, the glue layer 60 is removed and, optionally, the tape layer46 is deposited. In FIG. 4Q, a laser drilling process is performed toproduce the recess 58 and expose the redistribution layer bond pads 16from the redistribution layer 52. In an embodiment, the recess 58 passesthrough the tape layer 46, the buffer layer 44, and the passivationlayer 40. In FIG. 4R, individual bottom packages 14 are singulated fromone another.

In FIG. 4S, the top package 12 is mounted onto the bottom package 14. Inother words, a die bonding process is performed to reflow the solderfeatures 54. In an embodiment, the top and bottom packages 12, 14 areelectrically coupled together by reflowing the solder features 54. InFIG. 4T, the underfill 48 (or a sealing material, encapsulant, etc.),may optionally be inserted between or formed around the top and bottompackages 12, 14. Thereafter, as shown in FIG. 1, the PoP device 10 maybe mounted to the printed circuit board 32.

From the foregoing it should be recognized that the protrudingredistribution layer bond pads 16 provide beneficial features andadvantages. For example, the protruding redistribution layer bond pads16 permit a backside redistribution layer (RDL) to be formed in anIntegrated Fan Out Package on Package (InFO PoP) device, prevent cracksfrom occurring or propagating within the PoP device (e.g., between themolding compound and the metal via, at the backside RDL polymer, etc.),and so on.

An embodiment package on package (PoP) device includes a moldingcompound having a metal via embedded therein, a passivation layerdisposed over the molding compound, the passivation layer including apassivation layer recess vertically aligned with the metal via, and aredistribution layer bond pad capping the metal via, a portion of theredistribution layer bond pad within the passivation layer recessprojecting above a top surface of the molding compound.

An embodiment package on package (PoP) device includes a moldingcompound having a metal via embedded therein, a passivation layerdisposed over the molding compound, the passivation layer including apassivation layer recess vertically aligned with the metal via, a firstredistribution layer bond pad capping the metal via, and a secondredistribution layer bond pad vertically spaced apart from the firstredistribution layer bond pad by a portion of the passivation layer, aportion of the second redistribution layer bond pad within thepassivation layer recess projecting above a top surface of the moldingcompound.

An embodiment method of forming a through package via (TPV) for apackage includes embedding a metal via in a molding compound, forming apassivation layer over the molding compound, forming a passivation layerrecess in the passivation layer, the passivation layer recess verticallyaligned with the metal via, and capping the metal via with aredistribution layer bond pad such that a portion of the redistributionlayer bond pad within the passivation layer recess projects above a topsurface of the molding compound.

While the disclosure provides illustrative embodiments, this descriptionis not intended to be construed in a limiting sense. Variousmodifications and combinations of the illustrative embodiments, as wellas other embodiments, will be apparent to persons skilled in the artupon reference to the description. It is therefore intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A package on package (PoP) device, comprising: amolding compound having a metal via embedded therein; a passivationlayer disposed over the molding compound, the passivation layerincluding a passivation layer recess vertically aligned with the metalvia; and a redistribution layer bond pad capping the metal via, aportion of the redistribution layer bond pad within the passivationlayer recess projecting above a top surface of the molding compound. 2.The device of claim 1, wherein a second portion of the redistributionlayer bond pad is embedded in the molding compound.
 3. The device ofclaim 1, wherein a redistribution layer bond pad diameter is greaterthan a metal via diameter.
 4. The device of claim 1, wherein a portionof the passivation layer is disposed beneath the redistribution layerbond pad.
 5. The device of claim 1, wherein a buffer layer is disposedover the passivation layer, the buffer layer including a buffer layerrecess vertically aligned with the passivation layer recess and themetal via.
 6. The device of claim 1, wherein sidewalls of the portion ofthe redistribution layer bond pad projecting above the top surface ofthe molding compound are spaced apart from sidewalls of the passivationlayer.
 7. The device of claim 1, wherein a diameter of a top surface ofthe redistribution layer bond pad is less than or equal to a diameter ofa sidewall base of the redistribution layer bond pad.
 8. The device ofclaim 1, wherein a profile angle of the redistribution layer bond paddefined by sidewalls and a plane extending between a top surface of bondpad legs is between about forty degrees and about ninety degrees.
 9. Thedevice of claim 1, wherein a height of the redistribution layer bond paddisposed above the molding compound is greater than or equal to a heightof the passivation layer.
 10. The device of claim 1, wherein a diameterd1 of a top surface of the redistribution layer bond pad satisfies theformula: d1=d2−2[h1(tan θ₂)], where d2 is a diameter of a sidewall baseof the redistribution layer bond pad, h1 is a height of the passivationlayer, and θ₂ is a profile angle of the redistribution layer bond paddefined by sidewalls and a plane extending between a top surface of bondpad legs.
 11. The device of claim 1, wherein a diameter of theredistribution layer bond pad is greater than or equal to a diameter ofa sidewall base of the redistribution layer bond pad.
 12. The device ofclaim 1, wherein a diameter of the metal via is less than or equal to adiameter of a sidewall base of the redistribution layer bond pad. 13.The device of claim 1, wherein a top dimension of the recess is greaterthan a bottom dimension of the recess.
 14. The device of claim 1,wherein an open profile angle of the passivation layer defined bysidewalls of the passivation layer and a bottom surface of thepassivation layer is between about forty degrees and about seventydegrees
 15. A package on package (PoP) device, comprising: a moldingcompound having a metal via embedded therein; a passivation layerdisposed over the molding compound, the passivation layer including apassivation layer recess vertically aligned with the metal via; a firstredistribution layer bond pad capping the metal via; and a secondredistribution layer bond pad vertically spaced apart from the firstredistribution layer bond pad by a portion of the passivation layer, aportion of the second redistribution layer bond pad within thepassivation layer recess projecting above a top surface of the moldingcompound.
 16. The device of claim 15, wherein portion of the secondredistribution layer bond pad within the passivation layer recessincludes sidewalls, the sidewalls tapering from bottom to top.
 17. Thepackage of claim 15, wherein a diameter of the first redistributionlayer bond pad and a diameter of the second redistribution layer bondpad are each greater than a diameter of the metal via.
 18. A method offorming a through package via (TPV) for a package, comprising: embeddinga metal via in a molding compound; forming a passivation layer over themolding compound; forming a passivation layer recess in the passivationlayer, the passivation layer recess vertically aligned with the metalvia; and capping the metal via with a redistribution layer bond pad suchthat a portion of the redistribution layer bond pad within thepassivation layer recess projects above a top surface of the moldingcompound.
 19. The method of claim 17, further comprising forming thepassivation layer recess using a laser drilling process.
 20. The methodof claim 17, further comprising electrically coupling a printed circuitboard to a memory device using the redistribution layer bond pad.